The present invention relates to a film comprising a layer of a thermoplastic polymer having a fluorochemical hydrophilicity-imparting compound dispersed therein. In particular, the present invention relates to a film comprising a layer of polypropylene. The present invention also relates to a method of coating such film.
Films from extruded thermoplastic polymers, such as poly(alpha)olefins, are widely used in a variety of applications including, for example, as overhead transparencies, packaging materials and backing material for adhesive tapes. In many applications, the films need to be provided with one or more coatings. In order to provide good adhesion and coatability of such coatings, and particularly aqueous-based coatings, it is generally required to treat the film surface with a corona discharge before coating.
While this treatment is generally effective, it makes the film surface rough. Moreover, the effect of a corona discharge treatment on the film surface may degrade with time. Accordingly, corona discharge treatment is generally only useful if it can be done in line with the coating of the film. However, in a number of applications that may not be practical.
Accordingly, there is a need for a solution that can provide the thermoplastic polymer films with good coatability properties that can be maintained over a long period of time and that allow for coatings to be provided to the film with good adherence between the film and the coating. As will be set forth in detail below, the present invention solves this problem by dispersing a fluorochemical hydrophilicity imparting compound in the thermoplastic polymer layer of the film.
While the addition of certain fluorochemicals during the extrusion of thermoplastic polymers is known, the prior art does not disclose or suggest that the addition of a fluorochemical hydrophilicity imparting compound to an extruded thermoplastic polymeric film can provide good coatability properties to the film which can be maintained for a long period of time, nor does the prior art teach or disclose that good adhesion of the coating to the film can be obtained.
EP 0 516 271 discloses the use of a fluoroaliphatic group containing a compound in the extrusion of polypropylene fibers to impart durable wettability properties to the fiber""s surface. Particularly exemplified compounds are those that have a perfluorinated alkyl group linked to a poly(oxyalkylene) group terminated with a hydroxyl group or a lower alkyl ether.
WO 92/18569 and WO 95/01396 describe fluorochemical additives for use in the extrusion of thermoplastic polymers to prepare films and fibers with repellency properties. It is specifically disclosed that films can be prepared with good anti-wetting properties. It is further taught that polypropylene films with the fluorochemical dispersed therein have good antistatic properties.
U.S. Pat. No. 5,043,195 further describes a multi-layer sheet material including an electrically insulating film with a conductive layer on the upper surface and an antistatic layer carried by the lower surface. The antistatic layer comprises polyethylene and a fluoroaliphaticsulfonamide polyether compound.
U.S. Pat. No. 3,787,351 discloses the addition of polyethylene oxide containing fluorochemicals to self supporting structural filled or reinforced resinous shaped articles made of, for example, polypropylene. It is stated that the fluorochemical creates better bonding between fillers and the resin such that the amount of voids in the article is minimized.
The present invention provides a method of making a coated film comprising the steps of:
(A) providing a film comprising a layer of thermoplastic polymer having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I):
Rfxe2x80x94Qxe2x80x94Zxe2x80x94Xxe2x80x94T xe2x80x83xe2x80x83(I) 
wherein Rf represents a partially or fully fluorinated aliphatic group having at least 3 carbon atoms, Q is a linking group or a covalent bond, Z is a poly(oxyalkylene) group, X is oxygen or NR where R is a hydrogen atom or an alkyl or aryl group, and T is a hydrogen atom or an organic group having not more than 6 carbon atoms;
(B) applying a coating comprising at least one non-volatile component on said film; and
(C) when said coating contains volatile components, drying said coating to remove said volatile components from said coating.
In another aspect, this invention provides a film comprising a layer of thermoplastic polymer having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I) that is coated on at least one surface with a composition comprising at least one non-volatile component.
One preferred embodiment of the invention is a multi-layer film comprising a first and second layer of thermoplastic polymer, said first and second layer being in contact with each other, said second layer forming an outermost layer of said film and having dispersed therein a fluorochemical hydrophilicity imparting compound according to formula (I), and said first layer being substantially free of the fluorochemical hydrophilicity-imparting compound.
It has been found that the film of the invention can be readily coated without the need for prior treatments such as corona discharge. The film can be readily coated with an aqueous coating and good adhesion of the coating to the film can be obtained. Even films with smooth surfaces can be readily coatable. Finally, it was found that films can be obtained that are bright and highly transparent.
It will be understood that in connection with the invention the term xe2x80x9cdispersed thereinxe2x80x9d denotes merely the presence of the fluorochemical hydrophilicity-imparting compound in the thermoplastic polymer without limitation as to where the fluorochemical hydrophilicity-imparting compound is located in the layer. Thus, the fluorochemical hydrophilicity-imparting compound may be uniformly dispersed in the bulk of the polymer or a major portion of the fluorochemical hydrophilicity-imparting compound may have migrated to the surface of the thermoplastic polymer layer.
The films of the invention can consist of a single layer of thermoplastic polymer or the films can consist of multiple layers of thermoplastic polymer. In case the film is a single layer of thermoplastic polymer with the fluorochemical hydrophilicity imparting compound dispersed therein, both major surfaces of the film can be readily coated. When the film consists of multiple layers of thermoplastic polymer, various constructions are possible. For example, the film may consist of two layers of thermoplastic polymer and only one of them contains the fluorochemical hydrophilicity imparting compound. In such a film, the side of the multilayer film comprising the thermoplastic polymer layer with the fluorochemical hydrophilicity imparting compound will be readily coatable. Another embodiment of the film consists of three thermoplastic polymer layers whereby a core layer of thermoplastic polymer without the fluorochemical hydrophilicity imparting compound is provided on each side of a layer of thermoplastic polymer with fluorochemical hydrophilicity imparting compound. Such film is readily coatable on both sides.
Films with multiple layers of thermoplastic polymer are especially preferred in this invention because the above described properties of the film can be obtained without substantially impairing the mechanical properties of the film. Moreover, the properties can be obtained with less fluorochemical hydrophilicity imparting compound than would be needed in case of a film that consists of a single layer. Typically, a multilayer film will have one or two outer layers of thermoplastic polymer with a fluorochemical hydrophilicity imparting compound dispersed therein. The thickness of these outer layers may vary broadly, but it is typically no more than about 30 xcexcm, preferably between about 0.5 xcexcm and 30 xcexcm, and more preferably between about 1 xcexcm and 15 xcexcm. The thickness of the thermoplastic layer without the fluorochemical hydrophilicity imparting compound is typically selected to obtain the desired final total thickness of the film. Typically, the total thickness of the films of the present invention will be between about 10 xcexcm and 500 xcexcm, and more preferably between about 20 xcexcm and 250 xcexcm.
The films can be in the form of a web or they can be in the form of sheets. When desired, the films can be oriented monoaxially or they can be oriented biaxially. Surprisingly, multilayer films of the invention do not delaminate at the interface between layers containing fluorochemical hydrophilicity imparting compound and layers that do not contain the compound, even when the films are oriented by stretching in one or two directions.
Examples of thermoplastic polymers for use in the film include polyesters, polyurethanes, polyamides and poly(alpha)olefins. Preferred thermoplastic polymers are poly(alpha)olefins. Poly(alpha)olefins can include the normally solid, homo-, co- and terpolymers of aliphatic mono-1-olefins (alpha olefins) as they are generally recognized in the art. Usually, the monomers employed in making such poly(alpha)olefins contain about 2 to 10 carbon atoms per molecule, though higher molecular weight monomers sometimes are used as comonomers. The invention is applicable also to blends of the polymers and copolymers prepared mechanically or in situ. Examples of useful monomers that can be employed to prepare the thermoplastic polymers include ethylene, propylene, butene-1, pentene-1, 4-methyl-pentene-1, hexene-1, and octene-1, alone, or in admixture, or in sequential polymerization systems. Examples of preferred thermoplastic polymers include polyethylene, polypropylene, propylene/ethylene copolymers, polybutylene and blends thereof. Processes for preparing the thermoplastic polymers are well known, and the invention is not limited to a polymer made with a particular catalyst or process.
The fluorochemical hydrophilicity imparting compound is typically used in an amount of at least about 0.2% by weight based on the weight of the thermoplastic polymer and more preferably in an amount of at least about 0.5% by weight. The maximum amount of the fluorochemical hydrophilicity imparting compound is not critical; however, in case of a film consisting of only one layer of thermoplastic polymer, it is preferred to use the lowest amount possible so as not to impair the mechanical properties of the film. Generally, the amount of fluorochemical hydrophilicity-imparting compound is between about 0.3% by weight and 10% by weight, and more preferably between about 0.5% by weight and 6% by weight.
The fluorochemical hydrophilicity-imparting compound corresponds to formula (I) set forth above. In formula (I), Rf represents a partially or fully fluorinated aliphatic group having at least about 3 carbon atoms and preferably at least 4 carbon atoms. Rf is preferably a fluorinated, stable, inert, preferably saturated, non-polar, monovalent alkyl group. It can be straight chain, branched chain, or cyclic or combinations thereof. It can contain heteroatoms, bonded only to carbon atoms, such as oxygen, divalent or hexavalent sulfur, or nitrogen. Rf is preferably a fully-fluorinated alkyl group, but hydrogen or chlorine atoms can be present as substituents but preferably not more than one atom of either is present for every two carbon atoms. The R group has at least about 3 carbon atoms, preferably about 3 to 20 carbon atoms, and more preferably between about 6 carbon atoms and 20 carbon atoms. Rf preferably contains about 40% to 78% fluorine by weight, more preferably about 50% to 78% fluorine by weight. Most preferably, the terminal portion of the Rf radical is a perfluorinated moiety and contains at least 4 perfluorinated carbons, e.g., CF3CF2CF2CF213 , (CF3)2CFCF2xe2x80x94. Preferred Rf groups are preferably those perfluorinated alkyls according to the formula CnF2n+1 where n is about 4 to 14.
In formula (I), Q is typically an organic divalent or multivalent linking group or a covalent bond. Examples of Q groups include straight chain, branched chain or cyclic alkylene, arylene, aralkylene, oxy, sulfonyl, sulfoxy, amino, imino, sulfonamido, carboxyamido, carbonyloxy, urethanylene, ureylene, and combinations thereof such as sulfonamidoalkylene.
The Z group is a poly(oxyalkylene) group that can be depicted by the formula (ORxe2x80x2)x, where Rxe2x80x2 preferably is an alkylene group having about 2 to 4 carbon atoms, such as xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2xe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, and xe2x80x94CH(CH3)CH(CH3)xe2x80x94 or mixtures thereof, x is preferably a value from about 4 to 25, and more preferably from about 6 to 20. The oxyalkylene units in said poly(oxyalkylene) may be the same, as in poly(oxypropylene), or present as a mixture, such as in a heteric straight or branched chain of randomly distributed oxyethylene and oxypropylene units poly(oxyethylene-co-oxypropylene), or as in a straight or branched chain of blocks of oxyethylene units and blocks of oxypropylene units. The poly(oxyalkylene) chain can be interrupted by or include one or more catenary linkages. The water solubilizing group should provide sufficient hydrophilicity properties to the compound so as to obtain the beneficial hydrophilicity properties on the film. Accordingly, any catenary linkages in the water solubilizing group should not substantially impair the water solubilizing character of the Z group. Furthermore, it is preferred that the majority of oxyalkylene units are oxyethylene units. Thus in accordance with a particularly preferred embodiment, at least about 50% and more preferably at least about 60% of the number oxyalkylene units are oxyethylene units.
X and T together with Z represent the terminal, water-solubilizing portion of the fluorochemical hydrophilicity imparting compound. T is hydrogen or an organic group that has no more than about 6 carbon atoms, and preferably it has between about 1 to 4 carbon atoms. Examples of T groups include C1-C6 alkyl groups or xe2x80x94COR1 where R1 is an alkyl group of about 1 to 5 carbon atoms. X is oxygen or NR where R is a hydrogen atom or an alkyl or aryl group.
Examples of the residue, xe2x80x94Zxe2x80x94Xxe2x80x94T, in formula (I) include:
xe2x80x94(OCH2CH2)8xe2x80x94OH
xe2x80x94(OCH2CH2)6xe2x80x94OH
xe2x80x94(OCH2CH2)8xe2x80x94OCH3 
xe2x80x94(OCH2CH2)6xe2x80x94OCH3 
xe2x80x94(OCH2CH2)8xe2x80x94OCH2CH3 
xe2x80x94(OCH2CH2)6xe2x80x94OCH2CH3 
Particularly preferred fluorochemical hydrophilicity imparting compounds of the invention correspond to the following general formula (II):
Rfxe2x80x94Qxe2x80x94(OR2)ixe2x80x94(OR3)jxe2x80x94Xxe2x80x94T xe2x80x83xe2x80x83(II) 
wherein Rf, X, T and Q have the same meaning as defined in formula (I), R2 and R3 each independently can be selected from the group consisting of alkylene groups having about 2 to 4 carbon atoms, and i and j each represent a value of 0 to about 25 with the proviso that i+j is between about 4 and 25. Most preferably, R2 is ethylene and i is larger than j.
Specific examples of hydrophilicity imparting fluorochemical compounds include:
C8F17SO2N(C2H5)CH2CH2(OCH2CH2)7OCH3 
C8F17SO2N(C2H5)CH2CH2(OCH2CH2)9OCH2CH3 
C7F15SO2N(CH3)CH2CH2(OCH2CH2)7(OCH2CH(CH3))4OH
C8F17SO2N(C2H5)CH2CH2NHCH2CH2(OCH2CH2)9NHC(O)xe2x80x94CH3 
F(CF2CF2)nCH2CH2O(CH2CH2O)xH
wherein the last formula represents a mixture of compounds in which n is a number of about 2 to 6, and an average value of about 4, and x is about 14.
The hydrophilicity imparting fluorochemical compounds useful in the present invention can be prepared using known methods such as those described in U.S. Pat. No. 2,915,554 (Albrecht et al.). The Albrecht patent discloses the preparation of fluoroaliphatic group-containing, non-ionic compounds by reacting active hydrogen-containing fluorochemical intermediates, such as fluoroaliphatic alcohols (e.g. RfC2H4OH), acids (e.g., RfSO2N(Rxe2x80x2)CH2COOH), and sulfonamides (e.g., RfSO2N(Rxe2x80x2)H), with intermediates such as ethylene oxide, to yield, respectively, RfC2H4O(C2H4O)nH, RfSO2N(Rxe2x80x2)CH2CO2(C2H4O)nH, and RfSO2N(Rxe2x80x2)(C2H4O)nH, where n is a number greater than about 3 and Rxe2x80x2 is hydrogen or lower alkyl (e.g., 1 to 6 carbons). Analogous compounds can be prepared by treating the intermediates with propylene oxide or a mixture of ethylene oxide and propylene oxide. See also the fluoroaliphatic oligomers disclosed in U.S. Pat. No. 3,787,351 (Olson), and certain fluorinated alcohol and ethylene oxide condensates described in U.S. Pat. No. 2,723,999 (Cowen et al.).
The films of the present invention can be produced by extrusion of the thermoplastic polymer. Typically, a melt of the thermoplastic polymer is forced through an extrusion head with a rotating screw. The thermoplastic polymer composition can be extruded in thick form and cut into chips or granules for later use in extrusion (for example, like in a masterbatch), or can be directly extruded in a thin film. The extruded films can be mono- or bi-axially oriented by stretching the film in one or two directions that are orthogonal to each other. Typically, the stretch ratio is between 1:2 and 1:5.
In a preferred embodiment, the film is prepared by melting the thermoplastic polymer composition and then extruding it through a suitable distribution head and chilling the film between two rolls. Depending on the surface of these rolls, films can be produced that are smooth on both sides, rough on both sides or rough on one side and smooth on the other side. Examples of distribution heads for use in this invention include heads having two channels configured as an A-B-A configuration or an A-B configuration and distribution heads with three channels in an A-B-C configuration. By feeding the channels with different thermoplastic polymer compositions, multi-layer films can be obtained. For example, with an A-B-A configured distribution head, the B channel may be fed with pure thermoplastic polymer and the A channel with the composition of thermoplastic polymer and fluorochemical hydrophilicity imparting compound. With all channels open, a film will be obtained with a core layer of pure thermoplastic polymer provided on each side with a layer containing the composition of thermoplastic polymer and fluorochemical hydrophilicity imparting compound. Shutting off one of the A channels will result in a two-layer film one with and one without the fluorochemical hydrophilicity imparting compound. Alternatively, the film can be extruded in a blow extrusion which is typically used in the production of packaging film. The melt temperature used in the extrusion process is preferably selected such that the fluorochemical hydrophilicity imparting compound does not degrade or react. For the extrusion of the film, a single screw extruder can be used or a twin screw extruder with the screws counter-rotating or co-rotating. It is particularly preferred in this invention that the thermoplastic polymer composition, which includes the fluorochemical hydrophilicity imparting compound, is extruded in a twin screw extruder with counter rotating screws.
In one embodiment, in a first manufacturing step, using melt extrusion, chips or granules of the thermoplastic polymer and fluorochemical hydrophilicity imparting compound are prepared. These chips can then be used as an additive in the extrusion of a film or they can be used to extrude into a film. In a second step, the thermoplastic polymer fluorochemical hydrophilicity imparting compound chips or granules are used in a polymer extrusion feedstock along with chips or granules of the same pure thermoplastic polymer to produce a film.
The ratio of thermoplastic polymer to fluorochemical hydrophilicity imparting compound in the chip will vary based on the end use of the chip. In general, if the chip is to be extruded into a film or layer of a film without the addition of chips of pure thermoplastic polymer, less fluorochemical hydrophilicity imparting compound will be used than if the chip is to be diluted with pure thermoplastic polymer chips. In a preferred embodiment, the ratio of thermoplastic polymer to fluorochemical hydrophilicity imparting compound in the chip is between about 3:1 and 1000:1, and more preferably between about 20:1 and 4:1.
In accordance with the method of the present invention, the film is provided with a coating of a non-volatile component. As set out in detail above, at least one of the two major surfaces of the film is formed by a thermoplastic polymer layer that contains the fluorochemical hydrophilicity imparting compound. Such a surface is readily coatable with any type of coating, in particular aqueous coatings. In connection with this invention, the term xe2x80x9cnon-volatilexe2x80x9d means any type of compound that does not substantially vaporize under ambient conditions of temperature and pressure (about 25xc2x0 C. and about 1 atm). The coatings used in the invention may additionally contain volatile components that evaporate upon drying. Typically, such volatile components are used as a medium for applying the non-volatile components. Alternatively, the coating may consist of non-volatile components only. The film of the invention is particularly suitable for coatings that contain water and low viscosity aqueous coatings can readily be applied to the film. For example, aqueous coatings with a viscosity of less than about 10,000 cps or even less than 5,000 cps can be applied.
The coating of the present invention may be applied in a continuous or a discontinuous manner. In connection with the invention, the term xe2x80x9cdiscontinuousxe2x80x9d means that along at least one of two orthogonal axes that are in plane of the film, the coating is interrupted one or more times. In other words, along at least one of these axes there will be areas of the film surface that are covered and areas that are not covered. The term xe2x80x9ccontinuousxe2x80x9d means that the coating is not interrupted along the axes. However, the term continuous does not imply that the total film surface is covered by the coating.
The coating of the present invention can be applied by any coating technique known in the art. Examples of coating techniques include lamination, printing, gravure coating, knife coating, blade coating, bar coating, air knife coating, roll coating, reverse roll coating, knife over roll coating, wire wound rod coating and spray coating. The coating technique of choice will generally depend on the kind of coating that is to be applied.
According to an embodiment of the present invention, the film can be provided with an adhesive coating, for example an acrylic adhesive coating. Acrylic adhesives that can be applied are well known in the art and include adhesives that comprise a polymer containing an acrylic or methacrylic acid and an alkyl ester of an acrylic or methacrylic acid. Typically, the alkyl ester contains about 4 to 12 carbon atoms in the alkyl group. Examples of alkyl esters of acrylic or methacrylic acid include n-butyl, n-pentyl, n-hexyl, cyclohexyl, isoheptyl, n-nonyl, n-decyl, isohexyl, isobornyl, 2-ethyloctyl, isooctyl, n-octyl and 2-ethylhexyl acrylates and methacrylates. The acrylic adhesive polymer may contain further monomers to tailor the specific properties of the adhesives. Further details on adhesives and in particular acrylic adhesives can be found in Handbook of Pressure Sensitive Adhesive Technology, Edited by Donatas Satas, Second Edition 1989. The adhesive may be applied from an aqueous solution or non-aqueous solution.
The invention will now be illustrated by reference to the following examples, without however the intention to limit the invention thereto. All parts, ratios, percentages etc. in the following examples, are by weight unless otherwise noted.